Most people on this site keep female-only flocks, many of them in large runs rather than free range. Would you view that as a female prison? If so, I think it’s unfair to target rooster-only flocks in particular when you’re against same-sex flocks in general.
Once, my rooster flock and my mixed flock were let out by a family friend while I wasn’t home. When I got back, no one was dead. There was no blood bath. Things were tense, but the roosters did not fight to the death. In fact, many of them didn’t show interest in the hens. Roosters are always going to be flirtatious. That doesn’t mean they’re miserable when they don’t have a hen to flirt with. It seems that you’re anthropomorphizing; assuming that all roosters would want the same things you would personally want if you “were” a rooster. Since we can’t turn into chickens, I think it’s much better to base how they feel on how they act, rather than how we think we would act if we were them.